Migration of Animals
Birds do it. Fish do it. Mammals, insects, and reptiles do it. They migrate.
Migration is nearly universal within the animal kingdom; in fact, even sponges and jellyfish larvae move to adapt to imperfect habitats. Animals across the globe fly, swim, walk, or drift in their effort to find either food, a more hospitable climate, or places to breed.
These primal drives lead to arduous and often treacherous treks, some spanning thousands of miles.
Impressive trips
Humpback whales live in every ocean on Earth, and are near the top the list of mammals that migrate for long distances, traveling as much as 5,000 miles (8,047 kilometers) one way. Atlantic Humpbacks spend the winter feeding in the Caribbean Sea near Cuba. Each spring, they travel along the east coast of the United States to Labrador (in Canada) and on to Greenland. For humpback whales, the best place to feed isn't the best place to breed. During the warm months, these whales feed in nutrient-rich waters of the high latitudes. However, they mate and give birth in warmer waters that contain little food for them, so after these whales have journeyed as much as 5,000 miles (8,047 km) to their breeding grounds, they will fast (go without food) throughout the winter.
One large group of Monarch butterflies flutter 2,000 miles (3,219 km) from southern Canada through North and South Dakota, Nebraska, Kansas, Oklahoma, Texas, and into central Mexico. Another group of monarch butterflies migrate from Northern Maine, coming straight down the states of the Atlantic Coast, and then through all of the states of the Gulf Coast. They move through Montgomery County, and down into central Mexico.
However, out of all of the animals on Earth, none migrates farther than the sooty shearwater birds, which travel 40,000 miles each year as they fly around the Pacific Ocean in search of good feeding areas.
What are they thinking?!?!
So why do they do it? Migration is driven by a simple fact: Resources on Earth fluctuate. Warm summer months may be followed by inhospitable cold. Food may be abundant at some times of the year, but not at other times. The best place to give birth or hatch young may not be a good place to find food.
Why not find a shorter, simpler journey or stop altogether? "The simple answer is that the benefits of long-distance migration outweigh its cost and the benefits of shorter distances," said Hugh Dingle, a professor emeritus at the University of California. In other words, they do it because that’s how they find what they need.
Programmed to migrate
Natural selection shapes these journeys, and it has programmed this traveling nature into many animals, putting a destination in their genes. But the innate sense that points these migratory animals in the right direction has remained something of a mystery. This means that scientists do not know all of the details on how animals know where to go. Scientists do know, however, that migrants can use the sun, the stars, reflected light, the Earth's magnetic field, and their sense of smell to find their way.
Migrants have evolved to respond to cues, such as changes in day length, which tell them it's time to move. Waiting too long brings a number of risks, including losing the opportunity to stock up on food before departure or losing the competitive edge that comes with early arrival at your next habitat.
In addition to being pre-emptive, the travelers are focused. They don't meander, and they aren't distracted by food or mates along the way. The migrant generation of monarch butterflies is unable to reproduce until after it has reached its southern destination.
Single-mindedness makes sense, Dingle said. "If you get distracted, you are not going to get where you need to go."
Adaptations for Migration
Migratory animals that travel long distances have special adaptations to help them get there. The most obvious are birds. They have wings that allow them to fly long distances, their bodies are especially light (they have hollow bones) so they can stay high in the air, and they don't have unnecessary weight to carry around. Geese fly in formation, the shape of a "V", which decreases the wind drag on all the birds along both sides.
Birds add on extra fat stores to give them enough energy for long flights north and south, because they do not eat during the migration. Similarly, whales stock up well on food in the northern seas before heading south for the winter, because they don't eat on the way.
Meanwhile, migratory butterflies appear to have developed larger and more elongated wings. Butterflies that do not migrate often have smaller wings.
Animals that migrate have journeys that aren't easy: They go without food, swim upstream, fly nonstop, face hungry predators, and have to overcome barriers built by humans. The journeys may be fatal to some.
What does this have to do with Texas?
“Texas is a critical crossroads for so many species as they fly south to wintering grounds and then back north again," explains John Herron, director of conservation for The Nature Conservancy of Texas.
"Countless species fly and feed on the long trip from the tropics to breeding grounds in North America. In Texas each spring, we get to witness that epic journey as our trees and fields leaf out, providing food and sanctuary for millions of songbirds, hawks, and wading birds, all pushing relentlessly north to create the next generation of birds.
Here are just a few animals that migrate through Texas:
1. Golden-Cheeked Warblers
The golden-cheeked warbler is a very rare bird that migrates between Central America and Texas. These splendid black, white, and gold songbirds only breed and hatch their young in central Texas, making their nests in old-growth Ashe-juniper trees. They migrate to central Texas beginning in early March, then depart for their wintering ground in Nicaragua in mid-June. Federally endangered in the United States, the golden-cheeked warbler is threatened by habitat loss due to urbanization and nest parasitism by cowbirds.
2. Whooping Cranes
The migratory whooping crane is one of the most endangered birds on the planet, with a population of little more than 300 in the wild. The entire population of these birds breeds at Wood Buffalo National Park in northern Alberta, Canada, and migrates 2,400 miles south to winter haven at just a handful of locations along the Texas Gulf Coast. There, the birds spend the winter months feeding on blue crabs and other marine life. Along their migration route, whooping cranes rely on prairies and wetlands in Nebraska, Kansas and other states for stopover sites.
3. Mexican Free-Tailed Bats
One of the largest colonies of warm-blooded mammals on the planet makes its summer home near the small town of Mason, near Austin. Each May, the Eckert James River Bat Cave Preserve welcomes millions of female Mexican free-tailed bats, who use the cave to birth and raise pups before returning to Mexico in October.
While tranquil during the day, the cave grows into a bustling hive of activity in the evenings. In the hours before sunset, the bats grow restless—hundreds flutter and chirp around the mouth of the cave. A stream gradually emerges, spiraling upward to form a living “tornado of bats” that towers high above the cave. Eventually, the bats at the top of the spiral break off into columns that stream out over the countryside to feed—every night, each bat consumes nearly its body weight in mosquitoes and moths. The entire colony eats about 250 tons of insects every night. The colony flies to Mexico and Central America during the winter.
4. Black-Capped Vireos
A small songbird with distinctive white “spectacles,” the black capped vireo was added to the federal endangered species list in 1987. The song of this charming songbird has been called musical, emphatic, husky, harsh, chattering, restless, hurried, and even angry. Breeding in Texas, Oklahoma, Nebraska, and northeast Mexico, the birds nest in dense low thickets and oak scrub, usually on rocky hillsides. They arrive in Texas between late March and mid-April then depart for their winter grounds along the west coast of Mexico by mid-September.
At present, the breeding range extends from Oklahoma (where populations are spotty occurring only in 3 counties), south through the Edwards Plateau in central Texas, and down to Big Bend National Park, Texas, to wintering grounds along the west coast of Mexico.
5. Monarch Butterflies
The monarch butterfly’s distinctive coloring makes it one of the most easily recognized insects in the sky. Native to the Americas, the monarch has colonized such far-flung locales as western Europe and Australia. The life of the monarch butterfly is marked by a yearly generational migration. North America's western population migrates to California, while the eastern population—which can range as far north as Canada—migrates south, funneling through Texas and hugging the Gulf Coast down into Mexico.
At the terminus of the southern migration in central Mexico, tens of millions of butterflies spend the winter in less than 20 sites, gathering in 20-30 million per large site. They begin to disperse in late February and early March, mating and then flying north, usually making it to Texas before laying their eggs on milkweed plants. The next generation continues the migration, leapfrogging north until the third or fourth generation arrives as far north as Canada in May and June. This final generation migrates up to 2,200 miles back to Mexico, arriving in early November. They begin migrating singly, and then slowly gather into flocks as they converge upon roosting sites. During these migratory periods, monarch butterflies can be found on a variety of Texas locations.
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Migration Questions
Directions: Answer the following questions from the information you read about animals that migrate.
1. Name four methods of transportation that animals use to migrate.
2. How far do some humpback whales migrate round trip?
3. Some humpback whales spend the winter in the Caribbean Sea, even though there is not much of their type of food there. What is the purpose of them spending the winter there if there is not much food?
4. Name three countries that see Monarch butterflies migrate through them.
5. What type of animal migrates farther than any other animal on Earth? (Give the name of its species.)
6. Give three reasons why animals migrate.
7. Scientists don’t know all of the details on how animals know which direction to go when they migrate, but the scientists have some ideas on how the animals do it. Name some.
8. Give three ways that birds’ bodies are designed for long-distance travel.
9. What do birds and whales do similarly to prepare for migration, and why do they do it?
10. Give one way that migratory butterflies have different wings than butterflies that don’t migrate.
11. Name five animals that migrate through Texas.
12. Pretend you want to plan a trip to central Texas to see golden-cheeked warblers. What time of year should you go?
13. What man-made disaster could possibly wipe out the entire flock of whooping cranes when they migrate to their nesting spot in Texas?
14. Name two types of food that Mexican free-tailed bats eat.
15. Name three states in which black-capped vireos nest and breed.
16. How much food (in weight) does the bat colony in Mason, Texas, eat in one night?
17. Use a yellow pencil to draw an arrow on your map that shows the route of golden-cheeked warblers.
18. Use a blue pencil to draw an arrow on your map that shows the route of whooping cranes.
19. Use a brown pencil to draw an arrow on your map that shows the route of Mexican free-tailed bats.
20. Use a black pencil to draw an arrow on your map that shows the route of black-capped vireos.
21. Use an orange pencil to draw an arrow on your map that shows the route of monarch butterflies. (Get this information from page 1.)